Oakland Geology

I turned in the final version of my book manuscript the other day, and it’s been nice not having it on my mind all the time. (Follow along with the publishing process on the book’s page here.) But I had occasion to visit Middle Harbor Park this weekend, and as I walked up to this spot it brought to mind a little exchange I had with my editor. This is the replica pier made of reclaimed stones from the 1880s-era training wall.

I was writing about the work of building Oakland’s harbor, which has gone on since the 1850s and continues today. I mentioned that while the original estuary was completely replaced with “made land” and its counterpart, made water, there were now rocks — riprap — where before there had been only mud and sand. I contrasted the old original riprap to what they use today, with this pier in mind, and said that while the new stuff may work better, it has “little character.”

My editor wondered if I could explain that a little more. I decided not to for two reasons: (1) that would be a digression from what was already an aside and (2) the book has lots of examples of rocks with character.

But I came home thinking I’d been a little unfair. For one thing, our new riprap isn’t so monotonous; it’s mostly gray lava, but many of the rocks have veins and texture. Quarries in the Coast Range dig rocks that have gone through a lot, compared to the granites of the Sierra and those truly monotonous limestones of the Midwest. And the other thing is that the replica wall was made of carefully selected stones. It’s a work of art, not a work of work.

Next time you’re down there, look up the pier, at the south end of the beach. Walk on it and feel how solid it is underfoot, a standout piece of stonemasonry. It’s a real Oakland character. But also, check out the other riprap some time.

Oakland is full of rocks with character, and naturally so is this blog. Here are a few choice posts with examples from all over town:

The high-grade wall of Broadway Terrace

The decorative blueschist of Fairmount Avenue

The mastodon rubbing rocks of Tilden Park

The Knoxville conglomerate in Arroyo Viejo

Residential walls of local stones

And of course Big Rock at Lake Temescal

In fact, Oakland by my estimate has more natural rock types than any other city in the United States, making it America’s capital of lithodiversity

This last week I decided to make new assault on a puzzle I featured here back in 2008: What was the gigantic rock that gave Rockridge its name? I’m here to declare the controversy over, no thanks to me.

A few things have changed since then. One is that I ponied up for a subscription to newspapers.com to get full access to this primary historical material, a resource not easily available to previous researchers (or me). Another is that I’ve acclimated to newspaper writing from the Yellow Journalism era and realized how much of it was blatant shilling for advertisers and not to be trusted.

People in early Oakland had no city parks, other than the handful of public squares in the downtown area (most of which are still there). But the compact young city was surrounded by farms and open fields. It was easy for those with time and cash to spare to pack a picnic basket, ride one of the horse-drawn trolley lines to the edge of town and find a lovely spot to lounge and pass the day away from the smoke, dirt, fumes and horse manure that accompanied nineteenth-century civilization. In Oakland proper, one such place was the upper valley of Temescal Creek out by the Livermore estate, north of Mountain View Cemetery. (East Oaklanders favored the valley of Laundry Farm, now known as Leona Heights.)

The Livermores relocated to San Francisco and sold their estate, which was devoured by various developers over the years as the city below expanded. The Claremont Country Club and golf course got a big part, but the higher hills stayed idle longer. Then the Laymance Real Estate Company got hold of the high ground in the late 1900s decade and laid out the lots and streets of an exclusive suburb for wealthy white men, today’s Upper Rockridge.

Laymance had to muster up as much pompous puffery as possible, and its totem was an outcropping it named Cactus Rock. Here’s its icon in the first “Rock Ridge Gazette” weekly advertising feature, printed on the back page of the Oakland Tribune in March 1910.

Read that for a taste of what I mean by “puffery.” The Gazette went through at least twenty-one numbers in this vein.

Laymance brought parties of fashionably dressed people to the site and touted “the famous old Rock Ridge picnic grounds” to suggest memories of the good old 1870s. The promotional photo of one such party, draping themselves all over Cactus Rock, became the cover image of “Rockridge,” the Arcadia Press book by Robin and Tom Wolf. It looks huge on page 46. The rock’s image also appeared on Laymance’s lavish marketing pamphlet.

Today Cactus Rock is well hidden in a back yard overlooking Acacia Drive. Without a drone or access to the property, this is the best I can do to show it. It doesn’t look huge any more, but it still is, although maybe part of its base was removed.

After years of combing the area on foot, discounting imperfectly informed sources and tempting myself with the alternative of “Mount Ararat,” it’s finally clear to me that Cactus Rock was the subject of the old photo and the inspiration for the developers. “Rockridge Rock” is probably a legend in my own mind, suggested by taking the newspapers too seriously. I think the oldtime picnickers had lots of pleasant rocks to choose from.

Note that the drawing of Cactus Rock shows a clump of what looks like prickly pear at its base. Somewhere I have read that the first Spanish residents planted cactus near landmark boulders, in the early 1800s, and that a few ancient specimens are still around. That is to say, many rocks were “cactus rocks.” I hope a reader can retrieve that factoid for us.

Lakeside Park has undergone a lot of changes since Edson Adams put Oakland’s first golf course there. For one thing — and the thing behind this post — over the year the city has brought in rocks to a place that originally had none at all. Some of them are boulders that hold plaques: I won’t be talking about those. This is about the other ones, the working rocks who have the basic job of standing in your way, like the guard rocks down at Middle Harbor Park.

I take a walk around the lake every week, but this last week I took a few extra ones to visit all the working boulders. I think there are three generations of them. Here’s a selection.

The main road through Lakeside Park appears to have the first generation. My working theory is that the city parks department tapped a stash of rocks that were acquired on its own properties, principally Joaquin Miller and Leona Heights Parks. That accounts for the following mix of rock types. The majority belong to the Leona volcanics, probably sourced from Leona Heights Park. They present many different textures with an underlying lithology of light-colored, strongly altered volcaniclastic material that takes on an orange iron-oxide glaze with exposure. These five specimens illustrate the range of this rock unit.

The other boulders include nondescript ones I can’t confidently identify. Behind the rear lawn-bowling field is this laid-back hunk of what sure looks like Sierran granite.

But there’s a specimen of serpentinite, worth a close look, next to the Nature Center.

And right in front is the lake’s special star: this wild, glittering piece of blueschist.

Another generation of boulders sits along the path in front of Children’s Fairyland. It too consists of local stones: besides the Leona volcanics it includes proper sandstone belonging to, if I’m not mistaken, the Oakland Conglomerate in Joaquin Miller Park.

Near the entrance is a splendid serpentinite boulder.

And best of all are some good specimens of the ocher-bearing material from the Leona volcanics that the Ohlone tribes once prized.

The third generation of stones is of recent vintage, installed during the park’s bond-funded upgrade. Their main hangout is on the shore east of the boathouse by the parking lot.

Another grouping is in the brand-new Snow Park extension at the foot of 20th Street.

When these went in I thought they were sandstone (and said so here), but upon closer inspection I conclude that they’re some sort of welded tuff, not from anywhere in the Bay area, probably some place across the Central Valley or the desert beyond. That’s OK — Oakland welcomes immigrants. The material is fairly featureless, but these rare clasts look like bits of country rock that got torn off and taken up during the eruptive cataclysm that made this stone.

The lake shore also has plenty of cut and dressed stone, in the form of benches and curbs and capstones. They’re all commercial quarry granite, hardworking stuff that will last forever, but without the personality of real live boulders.